Distilled water and reverse osmosis (RO) purified water both remove contaminants but through fundamentally different processes with distinct tradeoffs. Distillation achieves higher purity (99.9%+ removal, 1-5 ppm TDS) but consumes 3.0-3.5 kWh per gallon at a cost of $0.54-$0.68 per gallon, while RO systems remove 93-99% of contaminants at just $0.03-$0.10 per gallon with minimal electricity but waste 4:1 to 2:1 water ratios.
The choice matters because drinking exclusively demineralized water may increase cardiovascular disease risk by removing protective minerals like magnesium, according to WHO guidance and peer-reviewed studies involving over 44,000 subjects. Understanding the regulatory standards, removal rates, health implications, and appropriate applications is essential for making an informed decision.
Whether you're choosing water for CPAP machines, daily drinking, or household appliances, this guide will help you understand which purification method makes sense for your specific needs. We'll examine federal regulations, compare technical performance, analyze health implications, and provide product recommendations based on third-party NSF certification standards.
đź“ś Federal Regulations & Standards
The FDA establishes the legal framework under 21 CFR Part 165.110, effective with major updates from January 2002 (disinfection byproducts), January 2006 (arsenic at 10 ÎĽg/L), and April 2022 (fluoride at 0.7 mg/L). Purified water must meet the United States Pharmacopeia standard from January 1, 1995, requiring maximum 10 ppm total dissolved solids.
This umbrella category includes water produced by distillation, deionization, reverse osmosis, or other suitable processes. When produced specifically by distillation, it may be labeled "distilled water." The FDA requires weekly microbiological testing with zero tolerance for E. coli and total coliform limits of 2.2 MPN per 100 mL using multiple-tube fermentation.
đź’§ FDA Purified Water Requirements:
- Maximum 10 ppm total dissolved solids (TDS)
- Produced by: distillation, deionization, RO, or suitable process
- Weekly microbiological testing required
- Zero E. coli tolerance
- Total coliform limit: 2.2 MPN per 100 mL
đź’§ Distilled Water Specifications:
- Subset of purified water produced specifically by distillation
- Typically achieves 1-5 ppm TDS (stricter than FDA minimum)
- Must meet all purified water standards
The EPA's Safe Drinking Water Act, amended most recently in 1996, sets National Primary Drinking Water Regulations applicable to public water systems. In April 2024, EPA finalized the first-ever PFAS standards at 4.0 parts per trillion for PFOA and PFOS—among the strictest contaminant limits ever established. Lead remains regulated at an action level of 15 μg/L (15 ppb), while arsenic must not exceed 10 μg/L.
NSF International, the Water Quality Association, and IAPMO R&T all certify products to NSF/ANSI standards with equal validity. NSF/ANSI 58 for reverse osmosis systems was updated in 2022 to require total PFAS reduction to ≤20 ppt (reduced from 70 ppt), while NSF/ANSI 53 now mandates lead reduction to ≤5 ppb when challenged with water containing 150 ppb lead—a tenfold safety margin. Distillation systems must meet NSF/ANSI 62 requirements for arsenic, chromium, mercury, nitrate, nitrite, bacteria, and protozoan cysts.
🔬 Removal Performance Comparison
Distillation removes 98-100% of arsenic regardless of pH, nearly 100% of microplastics, and 100% of bacteria and viruses through heat inactivation. The process leaves behind all heavy metals, minerals, and non-volatile compounds in the boiling chamber. However, volatile organic compounds with boiling points near or below 100°C may carry over with water vapor, which is why quality distillers include activated carbon post-filters achieving 95-99% chlorine removal.
Reverse osmosis demonstrates 98.5-99.1% lead removal in studies including a 2022 Bolivia pilot project, >90-99% PFAS removal confirmed by Duke University and NC State research showing near-complete elimination in under-sink systems, and 94-97% microplastic removal in seawater RO plants. A WHO-cited study found RO with membrane bioreactor systems achieved >95-99% pharmaceutical removal, with 20 of 27 compounds reduced below detection limits. The membrane's 0.001-micron pores block bacteria at >99.9999% (6-log minimum) per NSF P231 standards and viruses at >99.99% (4-log minimum).
Contaminant Removal by Technology
| Contaminant | Distillation | Reverse Osmosis | Standard Carbon |
|---|---|---|---|
| Lead | 98-100% | 98.5-99.1% | 0% (unless specialty) |
| Arsenic | 98-100% | 88-99% | 0% |
| PFAS | ~100% | 90-99% | Variable |
| Fluoride | Up to 99% | 85-99% | 0% |
| Bacteria/Viruses | 100% | >99.99% | 0% |
| Minerals (Ca, Mg) | ~100% | 90-97% | 0% |
| VOCs | 70-95% (w/ carbon) | 70-93% | 95-99%+ |
| TDS Reduction | 99.5%+ (1-5 ppm) | 90.8-97% (5-50 ppm) | 0% |
Key Insight: Distillation achieves highest purity but RO offers excellent removal at dramatically lower cost.
But RO shows critical gaps. Standard carbon filtration does not remove dissolved fluoride, requiring RO's 85-99% removal or distillation's up to 99% removal. RO membranes alone cannot remove chlorine and require carbon pre-filters, while the membrane allows some VOCs to pass through—a 2020 study showed 70-93% VOC removal depending on the specific compound. Total dissolved solids reduction reaches 90.8-97%, leaving 5-50 ppm TDS compared to distillation's 1-5 ppm.
Carbon filtration excels at its specialty—95-99%+ chlorine removal and highly effective VOC capture—but fails completely at dissolved solids, heavy metals (unless specially treated), fluoride, and microorganisms. UV treatment delivers 99.99% bacterial reduction at just 10-40 mJ/cm² but requires 400-1860 mJ/cm² for 4-log virus inactivation depending on virus type. UV adds no chemical contamination but removes nothing—particles, chemicals, and minerals pass through unchanged.
The ASTM D1193 standard for reagent water illustrates purity levels: Type I water requires ≤0.056 μS/cm conductivity, ≥18 MΩ-cm resistivity, and <50 ppb total organic carbon. Distilled water approaches Type II specifications, while RO water typically meets Type III standards. For pharmaceutical and laboratory applications, this distinction matters for regulatory compliance.
⚕️ Health Effects: WHO Warnings on Demineralized Water
The WHO convened expert consensus in Rome on November 11-13, 2003, concluding that "demineralised water without any further enrichment is not appropriate for drinking." Their recommended minimum standards specify 100 mg/L dissolved salts, 30 mg/L bicarbonate, and 30 mg/L calcium, with optimal levels of 40-80 mg/L calcium and 20-30 mg/L magnesium for cardiovascular protection. A 1980 USSR study cited by WHO found "definite adverse influence on the animal and human organism" from completely demineralized water.
⚠️ WHO Warning: Demineralized Water Health Risks
The World Health Organization's 2005 report identifies serious concerns with exclusive long-term consumption of demineralized water (distilled or heavily purified RO without remineralization):
Cardiovascular Effects (44,000+ subjects studied):
- Calcium in drinking water: protective effect 0.82 (95% CI = 0.70-0.95, p=0.008)
- Magnesium: even stronger protection 0.75 (95% CI = 0.66-0.86, p=0.000)
- Increased heart disease risk with low-mineral water
Bone Health (Multi-generational rat study):
- Significantly decreased femoral biomechanical properties
- Lower tibiae calcium and magnesium concentrations
- Reduced bone collagen turnover markers
- Lower vitamin D levels across three generations
Other Documented Effects:
- Increased pre-term birth and low birth weight risks
- Higher fracture rates in children
- Metabolic acidosis in infants (formula preparation)
- "Water intoxication" delirium after intense exercise
Critical Context: These risks apply to exclusive consumption without dietary mineral sources. Balanced diet typically provides adequate minerals.
A systematic review by Sunardi et al. published in Reviews on Environmental Health in 2022 analyzed 10 eligible studies from major databases spanning 2000-2022. The conclusion was unambiguous: "Demineralized water consumption in the long run was proven to lead to adverse effect" through lower quality of nutrient intake.
The cardiovascular evidence is substantial. A 2017 meta-analysis in the Journal of Water and Health following PRISMA guidelines analyzed approximately 44,000 subjects across multiple studies. Results showed calcium in drinking water provided a protective effect size of 0.82 (95% CI = 0.70-0.95, p=0.008) and magnesium showed even stronger protection at 0.75 (95% CI = 0.66-0.86, p=0.000) against cardiovascular disease.
Taiwan case-control studies provide compelling specific evidence. Yang's 1998 study in Stroke examined 17,133 cerebrovascular deaths versus 17,133 matched controls from 1989-1993. Magnesium levels of 7.4-13.4 mg/L showed an odds ratio of 0.75 (95% CI: 0.65-0.85), while levels above 13.4 mg/L reduced risk further to OR = 0.60 (95% CI: 0.52-0.70).
The bone health evidence from animal studies is alarming. A three-generation study published in PLOS ONE in 2015 followed 30 female rats per group continuously consuming tap water, bottled natural water, bottled mineralized water, or bottled purified water until 10 months of age across three generations. The purified water group showed significantly decreased femoral biomechanical properties, tibiae calcium and magnesium concentrations significantly lower than tap water, and significantly lower 1,25-dihydroxy-vitamin D levels.
Magnesium bioavailability from water is excellent. Verhas et al. demonstrated 59.1% ± 13.6% mean bioavailability using stable isotope tracing in 10 healthy men aged 25-42. A 2002 American Journal of Clinical Nutrition study found 45.7% ± 4.6% magnesium absorption from mineral water alone, increasing to 52.3% ± 3.9% when consumed with meals (p=0.0001). Calcium bioavailability from water reaches 25-45%, comparable to or exceeding food sources.
Important Counterpoint: The US Navy's experience provides counterbalancing evidence—sailors have consumed distilled seawater with TDS below 3 mg/L for approximately 40 years as of 2004, often for months continuously, with no known documented ill effects reported. This suggests that for healthy adults with adequate dietary intake, short to medium-term distilled water consumption poses minimal risk.
đź’° Cost Analysis & Environmental Impact
Home distillation consumes 3.0-3.5 kWh per gallon, requiring 4-6 hours at 500-800 watts continuous power draw. At the 2024 national average of $0.17 per kWh, producing one gallon costs $0.54-$0.68 in electricity alone. A family consuming one gallon daily spends approximately $248 annually just on electricity, or $20-23 monthly.
Initial equipment costs range from $200 for small portable units to $800 for premium countertop models, with large automatic systems reaching $1,300-$7,000. Maintenance is minimal—carbon filters every 3-5 months and monthly descaling—but distillers are remarkably durable with 25-40+ year lifespans reported.
Reverse osmosis systems cost $300-$700 installed for under-sink models, $200-450 for countertop units, and $4,800-$8,000 for whole-house systems. Operating costs are dramatically lower at $0.03-$0.10 per gallon, primarily reflecting water waste rather than electricity since most systems operate on water pressure alone. Filter replacement every 6-12 months costs $20-100 per filter, membrane replacement every 2-5 years runs $150-250, and total annual maintenance averages $50-250.
10-Year Total Cost Comparison (Family using 3 gallons/day)
| Method | Initial Cost | Annual Operating | 10-Year Total |
|---|---|---|---|
| Store-Bought Distilled | $0 | $1,095-1,643 | $10,950-16,430 |
| Home Distiller | $300-800 | $220-365 | $2,500-4,450 |
| Under-Sink RO | $300-700 | $50-250 | $800-3,200 |
| Countertop RO | $200-450 | $40-200 | $600-2,450 |
| Municipal Tap | $0 | $0.33 | $3.30 |
Breakeven Analysis: A $400 home distiller saving $0.90/gal (vs. $1.25 store price) pays for itself in 444 gallons or 5-6 months at 3 gallons daily.
Water Waste: RO's Environmental Consideration
Water waste in traditional RO systems follows a 4:1 to 5:1 ratio—four to five gallons wasted per gallon produced. This represents 20-25% efficiency, wasting approximately 4,380 gallons annually for a family using three gallons daily. Modern high-efficiency systems achieve 2:1 ratios (50% efficiency), while advanced tankless models reach 1.5:1 or even 1:1.
The EPA WaterSense specification finalized in December 2024 mandates a maximum 2.3:1 waste ratio for certified systems, expected to save 3.1 billion gallons nationally per year. Distillation produces zero wastewater—all input either becomes distilled water or evaporates.
Context: Daily Household Water Use
- Daily shower (10 min @ 2.5 gpm): 25 gallons
- Toilet flushes (5x daily @ 1.6 gpf): 8 gallons
- Washing machine cycle: 15-40 gallons
- RO rejected water (3 gal @ 4:1 ratio): 12 gallons
Key Insight: Drinking water represents approximately 1% of household water use. Rejected RO water can be reused for plants, outdoor cleaning, or toilet flushing rather than being truly wasted. Many households capture reject water for irrigation, effectively achieving zero waste.
Store-bought distilled water costs $1.00-$1.50 per gallon, resulting in $365-$547 annually for one gallon daily plus the environmental burden of 200+ plastic jugs. A $795 home distiller breaks even in 2-3 years compared to buying bottled, then continues saving money while eliminating plastic waste.
🏆 Best NSF-Certified Products
When evaluating water purification products, NSF certification provides independent verification of performance claims. Three accredited organizations certify to NSF standards with equal validity: NSF International, Water Quality Association (Gold Seal program), and IAPMO R&T (Research & Testing division).
Top Distillation Systems
đź’§ NSF/ANSI Standard 62 - Distillation Systems
What it certifies:
- TDS reduction (≤10 ppm target)
- Arsenic, chromium, mercury removal
- Nitrate and nitrite reduction
- Bacteria and protozoan cyst elimination
- Materials safety (no leaching)
For distillers, the Megahome MH943 series ($250-350) carries UL certification for electrical safety and produces one gallon in 5.5 hours using 580 watts, with 304 stainless steel construction and NSF-approved activated carbon filters. The Waterwise 4000 ($350-400) achieves faster production at one gallon in 4 hours using 800 watts, featuring superior 316-grade stainless steel boilers and CSA certification for USA and Canada.
Top Reverse Osmosis Systems
Among reverse osmosis systems, the iSpring RCC7AK ($230-280) stands out with full-system NSF/ANSI 58 and 372 certification by NSF International—not just component certification. This 6-stage 75 GPD system with alkaline remineralization achieves certified reduction rates of lead (98.9%), chromium (99.2%), fluoride (97.4%), selenium (99.0%), cadmium (98.8%), copper (97.8%), and PFAS (96-99%), with TDS reduction of 97.9%.
The APEC ROTL-A1000ALK ($500-700) represents the tankless category with IAPMO certification to NSF 372 and 58, producing 1000 GPD with a highly efficient 2:1 pure-to-drain ratio and alkaline remineralization. It achieves 99.9% certified removal of lead, arsenic, chromium, and PFAS.
AquaTru Classic ($400-450) solves the installation problem with a countertop design requiring no plumbing, earning IAPMO certification to NSF standards 41, 53, 58, 401, and P473—covering 83-84 contaminants including TDS, heavy metals, PFOA/PFOS, BPA, fluoride, radium, and cysts. The 4-stage system produces 11 cups in approximately 15 minutes with a 4:1 waste ratio (75-80% efficiency).
The Aquasana SmartFlow Reverse Osmosis ($500-600) carries WQA certification to NSF/ANSI 42, 53, 58, 401, and CSA B483.1—one of the most comprehensively certified systems available, removing 99.99% of 90 contaminants including fluoride, arsenic, chlorine, and lead.
🔍 Verification Tips: Avoid Marketing Deception
Red Flags - Not Real Certification:
- "Tested to NSF standards" (internal testing only)
- "Meets NSF standards" (no third-party verification)
- "NSF-quality materials" (materials claim, not performance)
- Component certification presented as system certification
How to Verify:
- Check NSF database: info.nsf.org/certified/dwtu
- Verify WQA certification: find.wqa.org
- Check IAPMO listings: pld.iapmo.org
- Look for specific standard numbers (NSF 58, 62, etc.)
- Verify certification covers YOUR concerns (lead, PFAS, etc.)
🎯 Usage Guide & Decision Framework
When to Use Distilled Water
Medical & Safety Applications (Non-Negotiable):
- CPAP machines - Manufacturer requirement; prevents mineral buildup and bacterial growth
- Neti pots/nasal irrigation - CDC recommends distilled, sterile, or boiled water to prevent deadly Naegleria fowleri infection
- Humidifiers - Eliminates "white dust" from aerosolized minerals
- Laboratory work - Required for ASTM compliance
- Kidney dialysis - Medical-grade purity prevents contamination
Household & Automotive:
- Steam irons - Prevents scale buildup
- Car batteries and cooling systems - Prevents corrosion and mineral deposits
- Baby formula - In areas with unsafe tap water
- Autoclaves - Medical sterilization equipment
Learn more about CPAP water requirements
When to Use Purified (RO) Water
Daily Drinking & Cooking (Preferred):
- Better taste due to retained trace minerals
- Provides cardiovascular-protective calcium and magnesium
- Costs 85-95% less per gallon than distilled ($0.03-$0.10 vs $0.54-$0.68)
- Faster production with continuous flow
- Ideal for coffee and tea brewing (minerals enhance extraction)
At-Risk Populations Should Prioritize Mineral Content:
- Children and adolescents (bone development needs)
- Pregnant or lactating women
- Elderly with marginal nutrition
- Athletes losing electrolytes through sweat
For contaminated well water with arsenic above EPA's 10 ÎĽg/L standard, lead from old plumbing, nitrate contamination, PFAS contamination, or microbiological issues, choose RO systems with comprehensive NSF/ANSI 53 and 58 certification achieving 98-99% removal of heavy metals, >90% PFAS elimination, and >99.9% pathogen removal.
Contaminant-Specific Filter Selection
| Your Concern | Best Solution | NSF Standard | Expected Removal |
|---|---|---|---|
| Lead in old plumbing | RO or certified carbon | NSF 53 | 98.5-99.1% |
| PFAS contamination | RO (must specify PFAS) | NSF 58 + P473 | 90-99% |
| Fluoride >2 ppm | RO or distillation | NSF 58 or 62 | 85-99% |
| Arsenic >5 ppb | RO or distillation | NSF 58 or 62 | 88-100% |
| Pharmaceuticals/BPA | RO with NSF 401 | NSF 401 | Up to 99% |
| Bacteria/viruses | RO + UV or distillation | NSF 58 + NSF 55 | >99.99% |
| Chlorine taste/odor | Carbon filter | NSF 42 | 95-99%+ |
| General improvement | RO with remineralization | NSF 42+53+58 | Comprehensive |
Key Insight: Match certification to YOUR specific contaminants. Not all RO systems are certified for all contaminants.
Installation & Budget Considerations
For Renters: Countertop options include the AquaTru Classic at $400-450 with comprehensive NSF certification for 83-84 contaminants, or countertop RO units from APEC or iSpring at $200-450. The Megahome distiller requires only counter space and a standard electrical outlet, needs no installation, and produces medical-grade water albeit slowly.
For Budget-Conscious Users: Under-sink RO systems at $300-700 installed deliver $0.03-$0.10 per gallon with annual maintenance of $50-250. Over 10 years, RO saves thousands of dollars for families consuming multiple gallons daily. However, for low-volume users needing occasional medical-grade water, buying bottled distilled at $1.00-$1.50 per gallon may be more economical than equipment purchase.
âś… Final Recommendations
The distilled versus purified water decision hinges on three factors: purity requirements of your specific application, your population health risk profile for mineral deficiency, and economic constraints around energy costs and water waste.
Choose Distillation When:
- Medical/lab applications require 99.9%+ purity
- CPAP, humidifiers, steam irons need mineral-free water
- Willing to pay $0.54-$0.68/gal for highest purity
- Can wait 4-6 hours per gallon production
- Need zero water waste (100% efficiency)
- Long-term investment (25-40 year lifespan)
Choose RO (Purified) When:
- Daily drinking water is primary use
- Cost matters ($0.03-$0.10/gal vs $0.54-$0.68)
- Want faster production (continuous flow)
- Value mineral retention for health
- Willing to manage filter replacements
- Can use/recapture reject water
Choose RO + Remineralization When:
- Daily drinking for at-risk populations
- Want contaminant removal + cardiovascular protection
- Following WHO mineral recommendations
- Children, elderly, or pregnant women in household
⚠️ Avoid Distilled as Sole Water Source:
- Children/teens in bone development years
- Pregnant or lactating women
- Elderly with marginal nutrition
- Athletes with high electrolyte loss
- Long-term exclusive consumption (>6 months)
- Without mineral-rich diet or supplements
Daily drinking and cooking favor modern RO systems offering 93-99% contaminant removal at $0.03-$0.10 per gallon while retaining or adding back minerals that provide cardiovascular protection with effect sizes of 0.75-0.82 in meta-analyses. The WHO's position that demineralized water "is not appropriate for drinking" without enrichment reflects genuine public health evidence, not theoretical concern.
For most households with safe municipal water, an under-sink RO system with NSF/ANSI 53 and 58 certification and remineralization provides optimal balance—removing concerning contaminants including lead (98.5-99.1%), arsenic (88-99%), PFAS (>90-99%), pharmaceuticals (up to 99%), and microplastics (94-97%) while maintaining or restoring beneficial minerals. Add a dedicated distiller for medical equipment, batteries, and applications demanding absolute purity.
The notion that water purification is binary—either completely pure or contaminated—misses the nuance that different water types serve different purposes optimally. Distillation for CPAP machines, RO with remineralization for drinking, and simple carbon filtration for improving tap water taste each occupy valid niches. Understanding the specific numeric performance of each technology, verified through NSF/WQA/IAPMO certification rather than manufacturer claims, enables informed matching of purification method to actual need.
Looking for more water quality resources? Check your local water quality in our city database, learn about specific contaminants in your water, or explore our complete filter guide to find the right system for your needs. For understanding your water quality report, see our comprehensive CCR guide.